1. Field of the Invention
The present invention relates generally to a method for using a rule base in a fuzzy logic controller.
2. Description of the Related Art
Fuzzy control, which uses fuzzy logic, is being used more and more in control-oriented processes. In addition to the software solutions using fuzzy logic, there are today also hardware solutions which are very general in their application and are intended for the most rapid and time-critical processes. In addition, these hardware solutions, which are in the form of microelectronic devices, should be small and use little power. The processing speed for the calculation of a sharp output value is thereby determined by the fuzzification, inference and defuzzification steps. A rule base is in general so constructed that several sharp output values are to be calculated thereby. The rules often deviate only minimally from one output to another.
From the German published patent application DE 42 25 758 A1, a circuit arrangement is known having a host computing unit, a fuzzy logic compressor and a knowledge base memory, in which at least one set of rules of a programmable number of rules, and in addition to a memory for a programmable number of input variables can be stored in the knowledge base memory. In this instance, it is disadvantageous that despite the similar construction of the corresponding rule base parts for the respective output variables, they each require rules of their own, and it is not possible to gain subsequent access to calculations that have already been carried out in the fuzzification and inference formation steps of one or more of the preceding rules having the same conditional part.
For the improving the processing speed, a method for accelerated rule evaluation in a fuzzy interface processor is known from the PCT patent application WO 95/08796, in which the conditions of the rules are checked one after the other for each input variable to determine whether the rules are fulfilled or not, and in which for a respective input variable only the conditions of those rules whose conditions were fulfilled for the preceding input variables are checked.